1. Field of the Invention
The present invention relates to a resin composition containing an ethylene-vinyl alcohol copolymer (hereafter may be abbreviated as “EVOH”) and a polyamide resin.
2. Description of the Related Art
Resin compositions of EVOH and polyamide resin have gas barrier properties, oil resistance, and solvent resistance, which are due to EVOH, as well as hot water resistance (retort resistance), which is due to polyamide resin (see, for example, JP 1-253442A). For this reason, these resin compositions serve many applications, such as films, sheets, containers for food packaging.
The film made of a resin composition of EVOH and polyamide resin often suffers from “cracks,” which may appear to be delamination, when a stress concentrates on the film as a result of bending, expansion/contraction, or the like, during retort sterilization. In view of this, a multilayer package in which appearance defects arising from bending of this resin composition under a high water content are suppressed has been proposed (see JP 6-23924A).
In the resin composition of EVOH and polyamide resin in a melted state, EVOH and polyamide resin react with each other. For this reason, if melt molding is performed for a long time, deterioration products of the resin are adhered to a discharge port or a screw of an extruder, or gels are produced in a molded product, making it difficult to continue the molding. That is, this resin composition has the problem of poor long-term run stability in melt molding. Another problem is that, if the molded product such as a film and a multilayer package contains gels, the molded product suffers from appearance defects such as delamination when it undergoes a process under severe conditions, such as a retorting process.
In order to solve these problems, various techniques have been proposed. For example, it has been proposed to improve melt-moldability by using a resin composition composed of EVOH and a polyamide resin in which a terminal carboxylic group has been modified into an N-substituted carboxylic amide group using a monoamine compound (see JP 5-1819B). It has also been proposed to improve hot water resistance and stretchability by using a resin composition composed of EVOH and a polyamide copolymer in which the amount of terminal amino groups is made less than the amount of terminal carboxyl groups by using a terminal controlling agent (see JP 4-178447A).
Also among the techniques that have been proposed are: techniques in which thermal stability in melt molding is improved by blending EVOH and a polyamide resin in which, using acid anhydride or the like, terminal amino groups are modified to be 30 μeq/g or less (see JP 5-140386A and JP 4-114060A), and a technique for improving shape-retaining properties during and after retort sterilization by blending EVOH and a polyamide resin modified with a diamine compound and a carboxylic acid (see JP 8-259756A).
Nevertheless, the above-described previous attempts to solve the problems have not yielded sufficient improvement effects, as will be shown in the later-described Comparative Examples.